Heretofore, the down-blending or dilution of hazardous or potentially hazardous feed materials to an acceptable target concentration has been relatively straight forward, i.e., to add the feed materials slowly and carefully to the dilution medium such as, for example, one might dilute concentrated H.sub.2 SO.sub.4 by adding it slowly to a relatively large amount of water such that the heat of reaction can be readily dissipated before the water is caused to erupt and splash about, or such as adding sodium metal slowly and carefully to an aqueous dilution system. Many such down-blendings have the potential for creating hazards, as do many chemical reactions carried out daily in industry. The techniques and safety equipment for minimizing such hazards are enormously varied and include safety measures and apparatus of enormous complexity.
The dangers of unforseen criticality events which are ever present with fissionable materials are in a different category from those attendant with conventional gasses, liquids or solids in that the immediate and residual effects of an uncontrolled fission accident can cause catastrophic consequences to the environment, both physical and economic, due to radiation release and can be felt by the surrounding population within a very short time of such incident and over vast areas. This being the case, Federal guidelines and requirements for equipment and-procedures for the handling of highly enriched uranium (HEU) and other such material have been promulgated and include requirements for fail-safe equipment and procedures requiring safety levels well above and beyond those afforded by electronically controlled pipeline valving, system flooding, automatic pump shut-down mechanisms and the like.
Objects therefore, of the present invention are: to provide an essentially fail-safe system, both method and apparatus, for the down-blending of feed material such as HEU (high-enriched uranium), plutonium, radium or thorium, or the like whereby the blending can only occur in safe proportions of feed material to dilution medium; whereby the primary safety or fail-safe mechanism is not dependent on the functioning of electronic controls, structural devices or the like; and to provide such system for performing the blending of a high-enriched uranyl nitrate hexahydrate, i.e., UO.sub.2 (NO.sub.3).sub.2 .cndot.6H.sub.2 O, hereinafter HE-UNH, with a natural, depleted, or slightly enriched uranyl nitrate hydrate (NUNH) solution to produce a low-enriched UNH solution.